I bought a plate to cover the rear opening where your breather is and installed my PVC valve there. You must have a breather somewhere; I use the
oil filler tube breather that fits in the intake. You also must baffle the PCV valve; I use on of these
Mr Gasket #5425:
I had to drill the hole in the plate larger (I think it had a 3/8 pipe thread in it originally), and if I remember correctly, used silicone to seal everything well.
Dan